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DIGESTION

Rondang R. Soegianto

2009

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Digestion: Physical process: Chewing, GI contraction

Chemical process: Digestive enzymes

Source of digestive enzymes: Exocrine glands - Salivary glands Pancreas Gallbladder Liver

Also cells and glands in mucosa

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Dietary Carbohydrate A. Polysaccharide: Plant carbohydrate: - Cellulose, present in diet but no digestive enzyme (cellulase) - Amylum consists of : Amylose (20%) α-1,4 links Amylopectin (80%) α-1,4 and α-1,6 links

for branching

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Animal starch- Similar to Amylopectin with more branches

STARCH and GLYCOGEN are polymers of glucose

Only one glucose residue has reducing group on C1 Other glucose residues are non-reducing ends

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B. Disaccharides Sucrose: Fruc + Gluc Lactose: Gluk + Galac Maltose: Gluk + Gluc

C. Monosaccharides: Gluc, Fruc, Galac Reducing sugars with reducing group on C1 or C2

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1.2 Carbohydrate Digestion Glycoside hydrolysis Monosach Intestinal mucosa

Digestive Enzymes: - Salivary α-amylase pH opt ~ 7.0 - Pancreatic α- amylase

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Salivary amylase stopped by acidity of stomach

Pancreatic amylase undergoes buffering action of Pancreatic juice and Bile in Small intestine

Continues digestion of starch and glycogen in food

Products: Oligosaccharides and disaccharide (maltose)

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2.1 Dietary Fat

Hydrophobic molecules

Major D F : Triacylglycerols = Esters of an alcohol (glycerol) and FA

In nature: 3 different FA in molecule structure

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2.2 Fat Digestion

a.Salivary and lingual lipases

For TAG with short to medium FA (cow’s milk) Product: 2-monoacylglycerols Help emulsify other fat in the diet

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b. In small intestine Bile salts emulsify fats Pancreatic lipase and co-lipase secreted from pancreas

Products: 2-monoacylglycerols + FA from C1 and C3

c. Formation of bile salts micelles Micelles contain: TAG, Monoacylglycerols, FA, Fat soluble vitamin

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g. Absorption of dietary lipids FA and 2-MAG packaged into micelles = micro droplets emulsified by bile salts. Also included in micelles: Cholesterol Fat soluble vitamis Micelles Microvilli Short and medium FA (C4 – C12) do not need bile salts for absorption. Enter portal blood directly.

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CLINICAL NOTE

Steatorrhea: lipid malabsorption increased lipid (including vit’s A, D, E, K and essential FA) in feces caused by disturbed lipid digestion and/or absorption

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i. Chylomicron formation

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j. Enterohepatic circulation of bile salts

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3.1 Digestion of Protein

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Activation of gastric and pancreatic zymogens

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